fix(server): Add error handler for webserver socket. (#3300)

Some times connection arrive, are given 404 responses, then disconnect,
resulting in ECONNRESET errors on the socket.  After we began monitoring
UncaughtExceptions, these errors show up. Suppress them with a handler
that ignores errors.

lib/server.js

@@ -123,6 +123,13 @@ class Server extends KarmaEventEmitter {
         BundleUtils.bundleResourceIfNotExist('context/main.js', 'static/context.js')
       ])
       this._boundServer = await NetUtils.bindAvailablePort(config.port, config.listenAddress)
+      this._boundServer.on('connection', (socket) => {
+        // Attach an error handler to avoid UncaughtException errors.
+        socket.on('error', (err) => {
+          // Errors on this socket are retried, ignore them
+          this.log.debug('Ignoring error on webserver connection: ' + err)
+        })
+      })
       config.port = this._boundServer.address().port
       this._injector.invoke(this._start, this)
     } catch (err) {
@@ -228,6 +235,10 @@ class Server extends KarmaEventEmitter {
 
       socket.on('complete', (data, ack) => ack())
 
+      socket.on('error', (err) => {
+        this.log.debug('karma server socket error: ' + err)
+      })
+
       socket.on('register', (info) => {
         let newBrowser = info.id ? (capturedBrowsers.getById(info.id) || singleRunBrowsers.getById(info.id)) : null
 
@@ -372,14 +383,19 @@ class Server extends KarmaEventEmitter {
     processWrapper.on('SIGINT', () => disconnectBrowsers(process.exitCode))
     processWrapper.on('SIGTERM', disconnectBrowsers)
 
-    processWrapper.on('uncaughtException', (error) => {
-      this.log.error(error)
+    const reportError = (error) => {
+      process.emit('infrastructure_error', error)
       disconnectBrowsers(1)
-    })
+    }
 
     processWrapper.on('unhandledRejection', (error) => {
-      this.log.error(error)
-      disconnectBrowsers(1)
+      this.log.error('UnhandledRejection')
+      reportError(error)
+    })
+
+    processWrapper.on('uncaughtException', (error) => {
+      this.log.error('UncaughtException')
+      reportError(error)
     })
   }
 

test/unit/server.spec.js

@@ -91,7 +91,7 @@ describe('server', () => {
     }
 
     mockBoundServer = {
-      on: sinon.spy((event, callback) => callback && callback()),
+      on: sinon.spy((event, callback) => callback && callback(mockServerSocket)),
       listen: sinon.spy((port, listenAddress, callback) => callback && callback()),
       close: sinon.spy((callback) => callback && callback()),
       address: () => { return { port: 9876 } }
@@ -148,6 +148,7 @@ describe('server', () => {
       server.start().then(() => {
         expect(NetUtils.bindAvailablePort).to.have.been.calledWith(9876, '127.0.0.1')
         expect(mockBoundServer.address).to.have.been.called
+        expect(typeof mockSocketEventListeners.get('error')).to.be.equal('function')
         done()
       })
     })